Building a network model is a complex task. It starts first with data extraction from the geographical information system (GIS) via a special interface. This will include and deliver all pipe data, node geographic coordinates and equipment forming the basic network structure. Control equipment such as valves and controlling regulators are read or derived from GIS data; regulator devices often must be connected manually or corrected afterwards.

Next the inputs and outputs of the network have to be introduced. Aside from feeder points or underground gas storage the outputs — better said the outflows — are modeled by consumers. Each consumer (up to hundreds of thousands) has his individual set of data, static or dynamic. Static data are used for long term planning for a certain scenario, dynamic data is used for short term planning (i. e. some days). When the simulation finally starts the correct pressure data — at least for the most important points — must be given to the simulator. Consumer data, valve position and pressure data must be taken from different IT-systems: Energy Data Management (EDM) system and Process Control system (SCADA).

To prove plausibility of the optimum PNS structure two scenarios were carried out, both for minimum as well as for maximum substrate cost situations. In the first case the maximum structure was reduced by taking away corn availability. With that only five substrate mixtures could be used for biogas production. The second scenario was set up to get an idea how feed — in tariffs can influence the outcome of an optimization. Therefore it was not allowed that a network set-up results e. g. in two 250 kWel CHPs if a 500 kWel instead could be taken.

4.3.1 Scenario I — No corn silage

As already mentioned in the beginning corn is currently a dominating substrate for biogas production. To show the potential of intercrops no corn is available in this scenario. Not to lose the comparability the amount of corn was compensated with an additional availability of intercrops. The calculation was based on the CH-outputs and adds up to additionally 904 t intercrops. With that 2,170 t/yr intercrops, about 1.7 times more than in the basic maximum structure shown in Figure 2, are available in the maximum structure of this scenario. Under these conditions PNS could choose between five different substrate feeds.

The optimization results in a technology network including two locations using the whole amount of available intercrops as shown in Figure 4.

location 1 and with same efficiency is supplied with substrate feed 2 consisting of 70 % intercrops and 30 % manure. It turned out that with this structure the outcome has yearly revenue of approx. 208,000 €. Compared to the optimum structure it is higher, but the basic conditions are different. Therefore this solution did not come up in the optimization of the maximum structure in the beginning. But it clearly shows that intercrops have a great potential to produce electricity and heat within a highly profitable biogas network without being in competition with food or feed production. But the precondition would be that in the case study a higher amount of intercrops is available as feedstock.

1.1.1 Biogas residue utilization status

The research results showed that biogas residue was one of the residue after organic matter anaerobic fermentation for biogas, which was mainly composed of undecomposed raw materials solid and new generation microbial biomass (Lin Jianfeng, 2003).As cellulose, hemicellulose, lignin and other substance of fermentation materials remained in the biogas residue in the fermentation process, so biogas residue basically retains all the components of anaerobic fermentation production besides the gas. Biogas residue generally contains organic matter 36% to 49.9%, humic acid 10.1% to 24.6%, crude protein 5% to 9%, total nitrogen 0.8% to 1.5%, total phosphorus 0.4% to 0.6%, and total potassium 0.6% to 1.2%. The requirement of N, P,K of anaerobic fermentation process is very low, therefore, the majority of N, P,K and other elements of fecaluria were not being used, and eventually left in the biogas residue and biogas slurry(Bian Yousheng,2005;Xie Tao, 2007). As microbial groups and undecomposed raw materials, so the biogas residue had its unique property (Zhang Quanguo, 2005).

Organic matter of biogas residue is not only a good fertilizer, but also conducive to microbial activity and the formation of granular structure, the organic matter surface can absorb amounts of soluble effective nutrients, under the soil microorganism’s action, it can continuously provide compatible nutrients for growing (Zhang Wudi, 2003). Currently, the utilization of biogas residue is mainly as following (Guo Qiang et al., 2005):

Soil OM decreases in crop soils in Europe and in other continents therefore using amendments for increasing the soil OM content has a particular interest.

Digestate contains high amount of volatile fatty acid (C2-C5) which could be decomposed within few days in the soil (Kirchmann & Lundwall, 1993). The greatest rate of decomposition were observed in the first day after the treatment (Marcato et al., 2009) but the mineralization rate were high during the first 30 days (Plaza et al., 2007). Moreover, the C-mineralization values from the soil incubation assay showed that the results of raw slurry were similar to the effect of compost being in the start of composting process while the digested slurry had similar C-mineralization rate in the soil samples than that of the matured compost (Marcato et al., 2009).

1.3 Effect of digestate on the microbiological activity of soil

Soil microbial community has an important role in the fertility of soil and its alteration after intervention to the soil (e. g. manuring, soil improving, soil pollution) could be indicate more sensitive these changes than changes in the soil physical and chemical properties.

Among the different organic wastes like compost, biogas residue, sewage sludge and different manures with and without mineral N, the biogas residue was more efficient for promoting the soil microbiological activity. The high amount of easy-degradable carbon increased the substrate induced respiration (SIR), which was enhanced by the higher carbon content resulted from the higher litter and root exudates of higher plant growth. In accordance with these results, the largest proportion of active microorganisms was found in the digestate treated samples (Odlare et al., 2008; Kirchmann, 1991). Similarly, the activity of invertase was significantly higher in the digestate treated samples than that in control ones (Makadi et al., 2006).

Besides the macro — and micronutrient content of digestate which are important not for the crops but for soil microorganisms too, it contains growth promoters and hormones, also. Therefore it could be used for stubble remains to facilitate their decomposing. Makadi et al. (2007) compared the effect of digestate and Phylazonit MC bacterial manure on the growth of silage maize (Zea mays L. ‘Coralba’) as a second crop after winter wheat and on the enzyme activities of soil. Digestate was used at the rate of 50% of the total N demand of silage maize while the Phylazonit MC was used at 5 L ha-1 dose. Their results of the changes in enzyme activities are summarized in Table 6.

The maximum of the degradation of disaccharides, indicated by the invertase activity, was found in the 3rd week after Phylazonit MC treatment, while it was found only after the 9th week in the digestate treated soil samples. The Phylazonit MC contains only bacteria and promoting agents of bacterial activity for degrading the soil OM. Contrarily, in the digestate treated samples the degradation of disaccharides takes place at similar rate through 9 weeks because of the OM content of digestate used. Changes in catalase activity indicate the effect of nutrient content of digestate to the increasing microbial metabolism.

A wood or steel structure in form of umbrella is built, and then a mesh network is relayed on the umbrella structure (Figs. 14 and 15). The air supported double membrane cover, which includes the gas holder, is mounted over the structure. The flexible membrane of the gas collector, i. e. holder, moves up and down as a function of the gas pressure. On the other hand, the storage tank covers are numerous: (1) closed cover (concrete, plastic, and tent), (2) straw cover, (3) granulate (perlite), (4) swimming vinyl covering, and (5) open as open lagoons and open storage tanks.

The technology that should be installed includes the filling indicator, tubes, measuring devices and meters, electricity network, fiber cables…etc. Afterwards, the gas collector should be installed as well as the excess and low pressure safeguard and the air support fan. Figure 16 shows an overview of the technology installation.

(a) MT-ENERGIE GmbH & Co. KG (b) BIOGAS NORD GmbH Fig. 16. Technology installation

Ways and means have been sought for many years to be able to produce oil-substitute fuel. Biodiesel extracted from fresh or used vegetable oil whether edible or not, is one such renewable alternative under consideration. Merits of biodiesel are that it can be directly used in engines with little or no modifications; contains little or no sulphur; no aromatics; has a higher cetane number and contains about 10% built-in oxygen and these properties help it burn fully with the result of having less carbon monoxide production, less unburnt carbon and less particulate matter residues. The production of biodiesel would be cheap as it could preferably be extracted from non edible oil sources. Jatropha curcas (Linaeus), a non­edible oil-bearing and drought-hardy shrub with ecological advantages, belonging to the Euphorbiaceae family, has been found to be the most appropriate renewable alternative source of biodiesel. Presently, the procedure for biodiesel production from jatropha seeds starts with harvesting whole ripe fruits. These fruits are then opened to remove the typically 3 or 4 seeds contained in each fruit. (A matured plant produces about 20kg of seeds in a year). These seeds are then sundried and afterwards stones, sticks, mouldy or damaged seeds and other foreign materials are handpicked from the batch of dried seeds. Next, this cleaned batch of seeds is crushed in an oil extraction machine to free the oil. This extracted oil is then filtered to remove impediments and the oil is poured in air-tight containers for storage. The extracted and filtered vegetable oil can be used directly as a fuel in suitable diesel engines without undergoing the trans-esterification process (Achten et al., 2008). However, to make it more useful in many engines, this Jatropha oil has to undergo a trans­esterification process of the triglyceride molecules in fats and oils with light weight alcohols like ethanol and methanol in a reactor in order to convert it to biodiesel. After being put into the reactor, the Jatropha oil settles; it is washed and purified by evaporation, and the liquid produced is biodiesel. Under optimal conditions, Jatropha curcas produces a higher oil yield per hectare compared to peanuts (Arachis hypogea), sunflower (Helianthus annus), soyabean (Glycine max), maize (Zea mays) and cotton (Gossypium species) (Kaushik et al., 2007). Biodiesel is a promising alternative because it is a renewable liquid fuel source that can be used alone and alternatively blended with petroleum-based diesel.

Jatropha’s potential as a new energy source comes at time when interest in biofuel production is at an all-time high. As observed by Parwira (2010), biofuel production could potentially position developing nations to become net exporters of fuel which could greatly advance their objectives of economic independence. The paper noted further that many

international corporations in Scandinavia, China, and Europe are purchasing tracts of land in developing countries (especially African countries) in an attempt to capitalize on this growth industry. New uses are being found for biofuel continually and this creates an impetus to strengthen efforts to produce them. In fact, several wireless communication companies have constructed cellular network base stations that are powered by Jatropha — based biofuel (Katembo and Gray, 2007). Presently, corn ethanol has a yield of 3100-4000 L/ha. This is still much higher than Jatropha curcas which is approximately 460-680 L/Ha of oil (Dar 2007). However, the production of Jatropha biodiesel is still very attractive largely due to its excellent fuel properties.

Kywe and Oo (2009) obtained a biodiesel yield of 30 gallons/day from a pilot plant which produced oil from Jatropha. The biodiesel demonstrated excellent fuel properties and it was found to be of very good quality. Tomomatsu and Swallow (2007) studied the economics and potential value of Jatropha curcas biodiesel production in Kenya and noted that in recent years, the production of Jatropha curcas has been widely promoted by private enterprises, non-governmental organizations and development agencies as one of the most viable candidates for biodiesel feedstock in Africa. While multiple benefits of jatropha production such as a petroleum product substitute, greenhouse gas mitigation and rural development are emphasized, the viability of production at farm level is questioned. The study revealed that the profitability of jatropha production for smallholder farmers is expected to be minimal unless farm-level production is accompanied by significant investments and policies targeted at enhancing production of the crop. However another economic study which took place in Mali showed that when all uses of Jatropha were taken into consideration, a rate of return of 135% could be achieved (Dinh et al., 2009).

Veljkovic et al., (2006) noted that biodiesel, which is made from renewable sources, consists of the simple alkyl esters of fatty acids. As a future prospective fuel, biodiesel has to compete economically with petroleum diesel fuels. The use of the less expensive feedstock containing fatty acids such as inedible oils, animal fats, waste food oil and byproducts of the refining vegetables oils reduces the costs of producing biodiesel. Therefore the availability and sustainability of supplies of less expensive feedstock will be a crucial determinant in competitively delivering biodiesel to commercial fuel filling stations. Such less expensive feedstock can come from inedible vegetable oils, mostly produced by seed-bearing trees and shrubs such as Jatropha curcas, a plant which has no competing food uses and which grows widely in tropical and subtropical climates across the world (Openshaw, 2000). Berchmans and Hirata (2008) developed a technique to produce biodiesel from crude Jatropha curcas seed oil having high free fatty acids (15% FFA). The high FFA level of the oil was reduced to less than 1% by a two-step pretreatment process. The first step was carried out with 0.60 w/w methanol-to-oil ratio in the presence of 1% w/w H2SO4 as an acid catalyst in 1-hr reaction at 500C. After the reaction, the mixture was allowed to settle for 2 hr and the methanol-water mixture which separated at the top layer was removed. The second step involved trans esterification using 0.24 w/w methanol to oil and 1.4% w/w NaOH to oil as alkaline catalyst to produce biodiesel at 650C. The final yield for methyl esters of fatty acids was achieved for 90% in 2 hr.

experiments. Experimental results revealed that a 12:1 molar ratio of methanol to oil, addition of 1.5% (w/v) CaO catalyst, 70°C reaction temperature, 2% water content in the oil produced more than 95% biodiesel yield after 3 hours reaction time. Calcium oxide activated with ammonium carbonate was an efficient super base catalyst for a high yield transesterification reaction and the base strength of CaO was more than 26.5 after dipping in ammonium carbonate solution followed by calcinations. Transesterification of Jatropha oil using supercritical methanol was also studied under the range of temperature from 120°C to 250°C, and range of pressure from 5 — 37 bars using superbase catalyst CaO and acid catalyst. The reaction products were analyzed for their content of glycerol by high performance liquid chromatography (HPLC) and this revealed that the process of supercritical transesterification achieved a yield of more than 95% after 1 hour.

The typical fuel properties of Jatropha curcas L, oil are as shown in Table 4 below. These properties show that jatropha biodiesel is a good quality biofuel.

Pseudoplastic fluids become thinner when the shear rate increases, until the viscosity reaches a plateau of limit viscosity. This behaviour is caused by increasing the shear rate and the elements suspended in the fluid will follow the direction of the current. There will be a deformation of fluid structures involving a breaking of aggregates at a certain shear rate and this will cause a limit in viscosity. For pseudoplastic fluids the viscosity is not affected by the amount of time the shear stress is applied as these fluids are non-memory materials i. e. once the force is applied and the structure is affected, the material will not recover its previous structure (Schramm, 2000). Some examples are corn syrup and ketchup.

1.2.1 Viscoplastic fluids

start flowing. One type of these, the Bingham plastic, requires the shear stress to exceed a minimum yield stress value in order to go from high viscosity to low viscosity. After this change a linear relationship between the shear stress and the shear rate will prevail (Ryan, 2003). Examples of Bingham plastic liquids are blood and some sewage sludge’s.

1.2.2 Dilatant fluids

Dilatant fluids become thicker when agitated, i. e. the viscosity increases proportionally with the increase of the shear rate. Like for the pseudoplastic fluids the stress duration has no influence, i. e. when the material is disturbed or the structure destroyed it will not go back to its previous state. Some examples of shear thickening behaviour are honey, cement and ceramic suspensions.

In general, all types of wastewater can be used as substrates as long as they contain carbohydrates, proteins, fats, cellulose and hemicelluloses as main components. It is important that the following points are taken into consideration when selecting the wastewater industrial.

The content of organic substance should be appropriate for the microorganisms selected in anaerobic process. [12]

in the bioreactor depends on the origin of the liquid. In the Table 8, is shows the methane production rate from wastewater of different types.

In all previous cases, the wastewaters are discharged directly into the body of water,

causing several environmental pollution in addition to the loss of the energetic potential

contained in the effluents.

The acetogenic step allows the transformation of the acids, resulting from acidonenic step to acetate, and carbon dioxide, by the action of the acetogenic bacteria. This operation is carried out by different types of bacteria.

2.2.2 Methanogenesis

The mehanogenic step consists of the transformation of acetate, hydrogen and carbon dioxide into methane. For that, there are two main system routes:

1. Aceticlastic methanogens : acetate + H2 ^ CO2 + CH4

2. Hydrogenotrophic methanogens: CO2 + 4 H2 ^ 2 H2O + CH4

There are other minor routes which have a low importance. In the anaerobic digesters, approximately 60 to 70% of methane are produced by the Aceticlastic methanogens routes (Oles, 1997).

The growth of methanogens bacteria is slow: 3 days in 35°C (Schink, 1997). As they are the most sensitive micro-organisms of the ecosystem, they govern the total kenetics of the process (Ramsay & Pullammanappallil, 2001). Moreover, they are sensitive to the presence of inhibitors such as VFA.

During the methanogenic phase, the products of fermentation such as acetate and H2 / CO2 are converted into CH4 and CO2 by methanogenic bacteria. Methanogenes bacteria can grow directly on H2 / CO2, acetate and all other compounds with only one carbon such as formate, methanol and the methylamine (Punal & al., 2003).

The methanogenic step is influenced by the operating conditions of the digester, such as temperature, hydraulic loading rate, organic loading rate, and the influent substrate composition (McHugh & al., 2003).

1.1.4 Materials and methods

1.1.4.1 Microorganisms

The yeast Saccharomyces cerevisiae B-4 obtained from Institute of Agricultural and Food Biotechnology Warsaw, Poland, was used for assessment ultrasound exposition to ethanol production. The yeast cultures were cultivated on YPG slants (2% glucose, 2% peptone, 1% yeast extract) supplemented with 2% agar, at pH 5.0 and 30 °C for 24 h. The active cultures
for inoculation were prepared by growing the yeast in a 1 L baffled shake-flask containing sterile water and 100 mL YPG medium at 30 °C for 24 h on orbital shaker table at 200 rpm to a concentration of approximately 108 cells mL-1. The cultures in baffled shaken flasks of 100 mL were used to prepare the inocula. After 24 h of incubation at 30 °С, the precultures were centrifuged at 3800 rpm for 10 min and the cells were resuspended in sterile water to obtain 106 cells mL-1. Enzyme |3-D-galactosidase (optimum temperature 30 °С, optimum acidity pH 4.5-5.0, activity 8.7 AU mg-1 d. m. of the preparation), from Aspergillus oryzae manufactured by the SIGMA company (USA), was used for co-immobilization process. The amount of yeast and enzyme was 3% free cell inoculum and 4 cm3 enzyme solution. The yeast culture was co-immobilized in the 2% (w/v) sodium alginate by dropping yeast and enzyme into 150 cm3 0.09 mol L-1 solution of CaCl2 with 10% glucose. The cell beads were washed with sterile water and were stored as a fermentation medium in physiological solution at 8°C.